A problem that arises in the manufacture of certain prior art FETs having a source/drain in the moat region and a channel stop under the field oxide is that the P+ or N+ channel stop impurity has a tendency to migrate under the field oxide toward and overlap the N+ or P+ source/drain of the transistor during processing, whereby the channel stop actually forms an undesirable P+N+ junction with the source/drain. Such migration also encroaches upon the channel region of MOSFET transistors, thereby undesirably decreasing the effective width of the transistor, as is well known. It is desired to eliminate or at least minimize these problems of the prior art by isolating the channel stop implant from the source/drain of the transistor being formed.